1. Field of the Invention
This invention relates to a process of making a synthetic detergent soap base from N-acyl sarcosine.
2. Description of the Prior Art
The use of sarcosinate surfactants, and in particular, N-acyl sarcosinates in the manufacture of soap is well known. Typically, the sarcosinate is used in the form of its sodium, potassium or ammonium salt solution. N-acyl sarcosinates are produced commercially by the Schotten-Baumann reaction of the sodium salt of sarcosine with the appropriate fatty acid chloride under carefully controlled conditions: ##STR1## where R is typically a fatty acid of chain length C.sup.10 to C.sup.18 commonly made from lauric, coconut, palmitic, myristic or oleic acid. After the reaction is complete, the crude sodium salt is acidified to liberate the free fatty sarcosinic acid which is separated from the aqueous by-products. It then is neutralized to a salt form. Sarcosinates such as sodium lauroyl sarcosinate, sodium cocoyl sarcosinate and sodium myristoyl sarcosinate are commercially available under the trademark HAMPOSYL.RTM. by W. R. Grace & Co.-Conn., as 30% active solutions in water. To produce soap bars, much of the water is removed, which may require heating the solution to temperatures in the vicinity of 150.degree. C.
Such sarcosinates are used, for example, in the skin cleansing compositions disclosed in U.S. Pat. No. 4,812,253. There it is disclosed that surfactants such as anionic acyl sarcosinates are present in the cleansing composition at a level of 20-70%, 20-50% in the case of soaps. In addition, sodium lauroyl sarcosinate is disclosed as being a preferred secondary surfactant together with sodium coco glyceryl sulfonate as a primary mild surfactant. The soap is disclosed as being made in situ from free fatty acids and a base selected from magnesium hydroxide, potassium hydroxide, sodium hydroxide and triethanolamine. Preferred fatty acids are mixtures of stearic and lauric acids having a ratio of from 2:1 to 1:1.
U.S. Pat. No. 4,754,874 to Haney discloses a transparent, mild, low pH soap bar and package therefor. The soap formulation disclosed includes sodium stearate and sodium cocoyl sarcosine, but no method of formulation is taught.
U.S. Pat. No. 4,954,282 to Rys et al. discloses skin cleansing compositions containing major amounts of acyl isethionates and at least one co-active surfactant, including sarcosinates.